Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease resulting in pancreatic ?-cell destruction. It is hypothesized that viral infections can trigger T1D progression by direct lysis of ? -cells and/or the induction of an exacerbated pro-inflammatory milieu consisting of reactive oxygen species (ROS), cytokines, and islet- infiltrating leukocytes. We recently demonstrated the importance of NADPH oxidase (NOX)-derived ROS synthesis on autoimmune diabetes, as Non-Obese Diabetic (NOD) mice unable to generate superoxide (NOD.Ncf1m1J) were highly resistant to spontaneous T1D. The resistance was partly mediated by dampened innate immune responses, as superoxide-deficient macrophages induced diminished levels of pro- inflammatory cytokines and Type I interferons upon Toll-like receptor 3 (TLR3) stimulation. The goal of this project will mechanistically define the role of ROS synthesis on macrophage differentiation and anti-viral responses in murine macrophages and human monocytes. We hypothesize that NOX-derived ROS synthesis is necessary for efficient pro-inflammatory M1 macrophage development/differentiation and viral-induced Type 1 diabetes. To address this hypothesis, the following independent and interrelated aims will be defined. (1) Determine the effects of superoxide on M1 and M2 macrophage development and function. (2) Establish the contribution of redox-dependent signals to anti-viral responses in macrophages. (3) Define the role of superoxide synthesis on bystander activation in response to viral infections. Collectively, these studies will define the fundamental roles of NOX-derived superoxide in macrophage development/differentiation in T1D and the regulation of innate immune responses to diabetogenic viruses. The knowledge gained from these studies may influence the novel design of therapeutic strategies for T1D prevention.